Forging device and forging method for outer joint member of constant-velocity universal joint

ABSTRACT

A forging apparatus includes an ironing mechanism and a phase alignment mechanism. The ironing mechanism includes: a punch set, which is fitted into a cylindrical portion of a pre-processing material to be formed into the outer joint member, and is radially expandable and contractible, the cylindrical portion having grooves formed in an inner peripheral surface thereof; and a die having a hole into which the cylindrical portion is press-fitted. The phase alignment mechanism is configured to align phases of the grooves in the inner peripheral surface of the pre-processing material and phases of track groove portion forming surfaces of the punch set with each other before the pre-processing material is fitted to the punch set.

TECHNICAL FIELD

The present invention relates to a forging apparatus and a forgingmethod for an outer joint member of a constant velocity universal joint.

BACKGROUND ART

In general, as illustrated in FIG. 29 , an outer joint member of aconstant velocity universal joint includes a mouth portion 132 havingtrack grooves 131 extending in an axial direction on an inner peripheralsurface thereof, and a shaft portion 133 provided to extend from abottom wall of the mouth portion 132. In this case, the track grooves131 of the mouth portion 132 each have an arc shape that is not inclinedin a circumferential direction, and a diameter of a track groove bottomat a center portion is set larger than a diameter of a track groovebottom on an opening side of the mouth portion 132. When the outer jointmember of the constant velocity universal joint having this structure isto be formed, cold ironing is generally performed.

As illustrated in FIG. 30 , a forging apparatus (cold ironing tool) isused for cold ironing. The cold ironing tool mainly includes a punch set142 and a die 123. The punch set 142 includes punches 120, a punch base121, and an umbrella punch 122. The punches 120 are capable of advancingand retreating in a direction inclined with respect to an axialdirection. The punch base 121 is configured to guide the punches 120.The umbrella punch 122 is configured to retain each of the punches 120at an axial position of the joint center. The die 123 is configured topress a pre-processing material 140. Track groove forming surfaces 147are formed on the punches 120.

Before the cold ironing, the pre-processing material 140 is formed bysub-hot forging, and is subjected to surface lubrication treatment (forexample, bonderizing treatment). The pre-processing material 140 isplaced on the punches 120, and an inner peripheral surface 123 a of thedie 123 presses an outer peripheral surface of the pre-processingmaterial 140. In this manner, the ironing is performed. After theironing, the forged product is held by the die 123 due to springback.Along with raising of the die 123, the forged product is raised whiledrawing the punches 120. As illustrated in FIG. 31A to FIG. 31B, thepunches 120 are radially contracted by being guided by the punch base121 that is inclined with respect to the axial direction, therebyattaining mold releasing of the forged product and the punches 120.

Incidentally, when the outer joint member as illustrated in FIG. 29 isto be formed by forging, the pre-processing material 140 as illustratedin FIG. 30 is used. The pre-processing material 140 has track forminggrooves 148 in an inner peripheral surface 141 of a cylindrical portion140 a. Then, when forging (ironing) is to be performed, it is requiredthat phases of the track forming grooves 148 of the pre-processingmaterial 140 and phases of the track groove forming surfaces 147 of thepunches 120 be aligned with each other.

In this case, the phases can be aligned with each other with use of apositioning mechanism as illustrated in FIG. 32 . The positioningmechanism includes a plate 151, a pair of phase alignment pins 153 and153, a pressing member (spring member) 154, and a shaft 155. The plate151 is configured to support the pre-processing material 140. The pairof phase alignment pins 153 and 153 are provided upright from a pinholder 152. The pressing member (spring member) 154 is configured toraise the pin holder 152 and the phase alignment pins 153 and 153through elastic pressing. The shaft 155 is configured to rotationallydrive. Further, the phase alignment pins 153 and 153 are insertedthrough a head 156 provided at a distal end portion of the shaft 155.Therefore, the head 156 rotates along with rotation of the shaft 155,and the phase alignment pins 153 and 153 rotate about an axial center ofthe shaft. The pressing member (spring member) 154 is suppressed in anurging force thereof by a stopper mechanism (for example, a cylindermechanism) (not shown).

Next, a positioning method for the pre-processing material 140 with useof the positioning mechanism illustrated in FIG. 32 is described. First,the positioning mechanism is brought into an initial state. The initialstate is a state in which the urging force of the pressing member(spring member) 154 is suppressed by the stopper mechanism, and the pairof phase alignment pins 153 and 153 provided upright from the pin holder152 are set so that distal ends thereof are located below the uppersurface of the head 156.

Then, the pre-processing material 140 is moved and is held at a positionconcentric with the head 156. In this state, an opening end surface 140a 1 of the cylindrical portion 140 a of the pre-processing material 140is placed on the plate 151. In this state, the urging force of thepressing member (spring member) 154 is released, and the pin holder 152and the phase alignment pins 153 and 153 are raised. In this case, whenphases of the raised phase alignment pins 153 and 153 match with phasesof the grooves 148 and 148 of the pre-processing material 140, the phasealignment pins 153 and 153 can be fitted into (inserted into) thecorresponding grooves 148 and 148 of the pre-processing material 140 asillustrated in FIG. 32 .

In contrast, when the phases of the phase alignment pins 153 and 153 andthe phases of the grooves 148 and 148 of the pre-processing material 140do not match with each other, the phase alignment pins 153 and 153cannot be fitted into (inserted into) the corresponding grooves 148 and148. Thus, the shaft 155 is rotated so that the phases of the phasealignment pins 153 and 153 and the phases of the grooves 148 and 148 ofthe pre-processing material 140 match with each other. With this, asillustrated in FIG. 32 , the phase alignment pins 153 and 153 can befitted into (inserted into) the grooves 148 and 148 of thepre-processing material 140.

After that, in the fitting state of the pins 153 and 153, thepre-processing material 140 is rotated through rotation of the shaft 155and is stopped at a position at which the phases of the pre-processingmaterial 140 are aligned with phases of the punches 120. In this state,as illustrated in FIG. 30 , the punch set 142 can be fitted into thecylindrical portion 140 a of the pre-processing material 140, and thecylindrical portion 140 a can be press-fitted into the inner peripheralsurface 123 a of the die 123, and be subjected to ironing.

Incidentally, the outer joint member of the constant velocity universaljoint has the following features as illustrated in FIG. 33 . Trackgrooves 131A and 131B of the outer joint member are grooves having anarc shape inclined with respect to an axial direction of a radiallyinner surface (inner peripheral surface) of the mouth portion 132.Inclination directions of the track grooves 131A and 131B adjacent toeach other in the circumferential direction are set to be mutuallyopposite to each other, and a diameter of a track groove bottom at acenter portion is set larger than a diameter of a track groove bottom onan opening side of the mouth portion 132.

When such an outer joint member 132 is to be formed, the pre-processingmaterial 140 as illustrated in FIG. 34A and FIG. 34B as described inPatent Literature 1 has hitherto been used. In this case, the functionand effect that “in the sub-hot forging for the pre-processing material,through use of the integral punch, increase in forging cost can besuppressed, and the accuracy of the track grooves can be enhanced” isobtained. As illustrated in FIG. 34A and FIG. 34B, the pre-processingmaterial 140 in this case has arc-shaped track groove surfaces 148Aa and148Ba having a substantially finished shape and being formed in asubstantially half part in an axial direction on a far side so as to beinclined in the circumferential direction, and linear track groovesurfaces 148Ab and 148Bb having a preliminary shape and being formed ina substantially half part in the axial direction on an opening side soas to be prevented from being inclined in the circumferential direction.In such a case, groove intervals at the opening of the pre-processingmaterial 140 are set to be equal.

In this case, the punch set 142 as illustrated in FIG. 34A and FIG. 34Bis used. The punch set 142 includes at least a plurality of punches 145,a punch base 146 configured to guide the punches 145 so as to be enableadvancing and retreating, and an umbrella punch 143. Each of the punches145 has a pair of track groove portion forming surfaces 147A and 147Bfor forming adjacent track grooves 148A and 148B.

CITATION LIST

-   Patent Literature 1: JP 2017-144452 A

SUMMARY OF INVENTION Technical Problem

FIG. 34A is an illustration of a case in which phases of the grooves148A (148Aa and 148Ab) and 148B (148Ba and 148Bb) of the pre-processingmaterial 140 and phases of the track groove portion forming surfaces147A and 147B of the punches 145 are aligned with each other. FIG. 34Bis an illustration of a case in which the phases of the grooves 148 ofthe pre-processing material 140 and the phases of the track grooveportion forming surfaces 147 of the punches 145 are not aligned witheach other. However, in the pre-processing material 140 illustrated inFIG. 34A and FIG. 34B, the groove intervals at the opening are set to beequal. Therefore, even when the phases of the grooves 148A (148Aa and148Ab) and 148B (148Ba and 148Bb) of the pre-processing material 140 andthe phases of the track groove portion forming surfaces 147A and 147B ofthe punches 145 are not aligned with each other, the the phase alignmentpins 153 and 153 illustrated in FIG. 32 can be fitted.

Therefore, even when the pre-processing material 140 is positioned withthe positioning mechanism as illustrated in FIG. 32 , the phases of thegrooves 148A and 148A of the pre-processing material 140 and the phasesof the track groove portion forming surfaces 147A and 147A of thepunches 145 are not aligned with each other in some cases. It is notpossible to stably form the outer joint member 132 in which the trackgrooves 131A and 131B each have an arc shape inclined in thecircumferential direction, and the diameter of the track groove bottomat the center portion is set larger than the diameter of the trackgroove bottom on the opening side as illustrated in FIG. 33 .

The present invention has been made in view of the above-mentionedproblem, and provides an forging apparatus and a forging method for anouter joint member, which enable stable formation of an outer jointmember in which track grooves each have an arc shape inclined in acircumferential direction, and a diameter of a track groove bottom at acenter portion is set larger than a diameter of a track groove bottom onan opening side, and enable use of an existing ironing apparatus as itis.

Solution to Problem

According to one embodiment of the present invention, there is provideda forging apparatus for an outer joint member of a constant velocityuniversal joint, the constant velocity universal joint comprising: anouter joint member having a spherical inner peripheral surface in whicha plurality of track grooves are formed; an inner joint member having aspherical outer peripheral surface in which a plurality of track groovesare formed so as to be paired with the track grooves of the outer jointmember; a plurality of balls, which are interposed between the trackgrooves of the outer joint member and the track grooves of the innerjoint member, and are configured to transmit torque; and a cage, whichis interposed between the spherical inner peripheral surface of theouter joint member and the spherical outer peripheral surface of theinner joint member, and is configured to hold the balls, the trackgrooves of the outer joint member and the track grooves of the innerjoint member each having an arc-shaped ball raceway center line having acurvature center that is prevented from being offset in an axialdirection with respect to a joint center, a plane including the ballraceway center line and the joint center being inclined in acircumferential direction with respect to a joint axial line, each ofthe track grooves of the outer joint member and each of the trackgrooves of the inner joint member, which are paired with each other,being inclined in mutually opposite directions, the forging apparatuscomprising: an ironing mechanism comprising: a punch set, which isfitted into a cylindrical portion of a pre-processing material to beformed into the outer joint member, and is radially expandable andcontractible, the cylindrical portion having grooves formed in an innerperipheral surface thereof; and a die having a hole into which thecylindrical portion is press-fitted; and a phase alignment mechanismconfigured to align phases of the grooves in the inner peripheralsurface of the pre-processing material and phases of track grooveportion forming surfaces of the punch set with each other before thepre-processing material is fitted to the punch set, the phase alignmentmechanism comprising: a phase alignment jig comprising a pair of convexportions, which are to be fitted into grooves of the pre-processingmaterial which are adjacent to each other in the circumferentialdirection under a state in which the phases of the grooves in the innerperipheral surface of the pre-processing material and the phases of thetrack groove portion forming surfaces of the punch set are aligned witheach other, and are restricted from being fitted thereto under a statein which the phases of the grooves in the inner peripheral surface ofthe pre-processing material and the phases of the track groove portionforming surfaces of the punch set are not aligned with each other; and arotary mechanism configured to rotate the pre-processing materialaligned in the phases by the phase alignment jig about an axial centerof the pre-processing material so as to align the phases of thepre-processing material with the phases of the track groove portionforming surfaces of the punch set.

With the forging apparatus for an outer joint member of a constantvelocity universal joint according to the present invention, before thepre-processing material is fitted to the punch set, the phases of thegrooves in the inner peripheral surface of the pre-processing materialand the phases of the track groove portion forming surfaces of the punchset can be aligned with each other by the phase alignment mechanism.Thus, in the ironing mechanism, under the state in which the phases ofthe grooves of the pre-processing material and the phases of the trackgroove portion forming surfaces of the punch set are aligned with eachother, the punch set can be fitted into the cylindrical portion.Further, the ironing mechanism comprises the punch set that is fittedinto the cylindrical portion and is radially expandable andcontractible, and the die having the hole into which the cylindricalportion is press-fitted. Accordingly, an existing ironing mechanism(forging apparatus) can be used as it is.

Further, it is preferred that, in an inlet portion of the innerperipheral surface of the cylindrical portion, portions of thepre-processing material each between the grooves adjacent to each otherin the circumferential direction be thin portions or thick portions, andthe thin portions and the thick portions be alternately arranged alongthe circumferential direction, and that the phase alignment mechanismcomprise a phase alignment jig comprising: a pair of convex portions tobe fitted along the axial direction to the grooves of the pre-processingmaterial which are adjacent to each other in the circumferentialdirection; and a coupling portion, which is formed between the convexportions, is allowed to be internally fitted to corresponding one of thethin portions of the pre-processing material along the axial direction,and is prevented from being internally fitted to corresponding one ofthe thick portions of the pre-processing material along the axialdirection.

With such setting, under the state in which the coupling portion of thephase alignment jig is fitted to the pre-processing material, the phasesof the grooves of the pre-processing material can be set to desiredphases. Therefore, the phases of the grooves of the pre-processingmaterial and the phases of the track groove portion forming surfaces ofthe punch set can be stably aligned with each other through rotation ofthe pre-processing material by the rotary mechanism.

It is preferred that the phase alignment jig of the phase alignmentmechanism comprise at least two phase alignment jigs arranged oppositeto each other at 180° with respect to the axial center. With use of thetwo phase alignment jigs as described above, phase alignment is stablyperformed.

The punch set may comprise: at least a plurality of punches; and a punchbase configured to guide the punches so as to enable advancing andretreating, and each of the punches may have a pair of forming surfacesfor forming the adjacent track grooves.

The punch set may comprise an umbrella punch in addition to the punchesand the punch base.

The punches and the punch base may be received and guided into a punchholder, and a length of an advancing stroke of the punches may be largerthan a length of an advancing stroke of the punch base.

The inner peripheral surface of the cylindrical portion of thepre-processing material may have: an arc-shaped track groove surfacehaving a substantially finished shape and being formed in asubstantially half part in an axial direction on a far side so as to beinclined in the circumferential direction; and a linear track groovesurface having a preliminary shape and being formed in a substantiallyhalf part in the axial direction on an opening side so as to beprevented from being inclined in the circumferential direction.

An outer peripheral surface of the cylindrical portion of thepre-processing material may have a protruding portion that partiallyprojects.

According to one embodiment of the present invention, there is provideda forging method for an outer joint member of a constant velocityuniversal joint, the constant velocity universal joint comprising: anouter joint member having a spherical inner peripheral surface in whicha plurality of track grooves are formed; an inner joint member having aspherical outer peripheral surface in which a plurality of track groovesare formed so as to be paired with the track grooves of the outer jointmember; a plurality of balls, which are interposed between the trackgrooves of the outer joint member and the track grooves of the innerjoint member, and are configured to transmit torque; and a cage, whichis interposed between the spherical inner peripheral surface of theouter joint member and the spherical outer peripheral surface of theinner joint member, and is configured to hold the balls, the trackgrooves of the outer joint member and the track grooves of the innerjoint member each having an arc-shaped ball raceway center line having acurvature center that is prevented from being offset in an axialdirection with respect to a joint center, a plane including the ballraceway center line and the joint center being inclined in acircumferential direction with respect to a joint axial line, each ofthe track grooves of the outer joint member and each of the trackgrooves of the inner joint member, which are paired with each other,being inclined in mutually opposite directions, the method comprising:aligning, before the pre-processing material is fitted into a punch set,phases of grooves formed in an inner peripheral surface of a cylindricalportion of the pre-processing material and phases of track grooveportion forming surfaces of the punch set with each other with use of aphase alignment mechanism; and performing ironing by fitting the punchset that is radially expandable and contractible into the cylindricalportion of the pre-processing material of the outer joint membercomprising the cylindrical portion under a state in which the phases arealigned with each other, and press-fitting the cylindrical portion intoa hole of a die, and the phase alignment mechanism comprising a phasealignment jig comprising a pair of convex portions, which are to befitted into two grooves of the pre-processing material which areadjacent to each other in the circumferential direction under a state inwhich the phases of the grooves in the inner peripheral surface of thepre-processing material and the phases of the track groove portionforming surfaces of the punch set are aligned with each other, and arerestricted from being fitted thereto under a state in which the phasesof the grooves in the inner peripheral surface of the pre-processingmaterial and the phases of the track groove portion forming surfaces ofthe punch set are not aligned with each other.

With the forging method for an outer joint member of a constant velocityuniversal joint according to the present invention, under the state inwhich the phases of the grooves of the pre-processing material(pre-processing material in which the grooves each have an arc shapethat is inclined in the circumferential direction, and a diameter of atrack groove bottom at the center portion is set larger than a diameterof a track groove bottom on an opening side) and the phases of the trackgroove portion forming surfaces of the punch set are aligned with eachother, the punch set can be fitted into the cylindrical portion.Therefore, under the state in which the phases of the grooves and thephases of the track groove portion forming surfaces of the punch set arealigned with each other, the cylindrical portion of the pre-processingmaterial can be press-fitted into the hole of the die and be subjectedto ironing.

It is preferred that, in an inlet portion of the inner peripheralsurface of the cylindrical portion, portions of the pre-processingmaterial each between the grooves adjacent to each other in thecircumferential direction be thin portions or thick portions, and thethin portions and the thick portions be alternately arranged along thecircumferential direction, and that the phase alignment mechanismcomprise a phase alignment jig comprising: a pair of convex portions tobe fitted along the axial direction to the grooves of the pre-processingmaterial which are adjacent to each other in the circumferentialdirection and a coupling portion, which is formed between the convexportions, is allowed to be internally fitted to corresponding one of thethin portions of the pre-processing material along the axial direction,and is prevented from being internally fitted to corresponding one ofthe thick portions of the pre-processing material along the axialdirection.

With such setting, under the state in which the coupling portion of thephase alignment jig is fitted to the pre-processing material, the phasesof the grooves of the pre-processing material can be set to desiredphases (groove portion forming surfaces of the punch set).

It is preferred that, under a state in which the pair of convex portionsof the phase alignment jig are fitted to a pair of grooves of thepre-processing material, and a radially outer surface of the phasealignment jig is internally fitted to the corresponding one of the thinportions, the pre-processing material is stopped at a predeterminedphase position through rotation of the phase alignment jig, and ironingwith the punch set and the die is performed. With such setting, thephases of the grooves of the pre-processing material and the phases ofthe track groove portion forming surfaces of the punch set can be stablyaligned with each other through rotation of the pre-processing material.

In the ironing, the cylindrical portion of the pre-processing materialcan be press-fitted into the hole of the die from an opening portionside of the cylindrical portion.

Advantageous Effects of Invention

According to the present invention, under the state in which the phasesof the pre-processing material (pre-processing material in which thegrooves each have an arc shape that is inclined in the circumferentialdirection, and the diameter of the track groove bottom at the centerportion is set larger than the diameter of the track groove bottom onthe opening side) and the phases of the track groove portion formingsurfaces of the punch set are aligned with each other, the cylindricalportion of the pre-processing material can be press-fitted into the holeof the die and be subjected to ironing. Accordingly, forming failure,die breakage, and the like can be prevented. In addition, as a moldingdevice (ironing mechanism), an existing apparatus can be used as it is,thereby being capable of attaining cost reduction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a main part of a forging apparatus foran outer joint member of a constant velocity universal joint accordingto the present invention under a state in which phase alignment isperformed with use of a phase alignment mechanism.

FIG. 2 is a perspective view of a main part of the phase alignmentmechanism illustrated in FIG. 1 .

FIG. 3 is an end view of the pre-processing material.

FIG. 4 is a front view of the pre-processing material.

FIG. 5 is a perspective view of a phase alignment jig.

FIG. 6 is an end view of a state in which the phase alignment jigscannot be fitted to the pre-processing material.

FIG. 7 is an end view of a state in which the phase alignment jigs arefitted to the pre-processing material.

FIG. 8 is a front view for illustrating a punch set of an ironingmechanism.

FIG. 9A is an illustration of a relationship between the punch set ofthe ironing mechanism and the pre-processing material, and is a frontview of a state in which phases are aligned with each other.

FIG. 9B is an illustration of a relationship between the punch set ofthe ironing mechanism and the pre-processing material, and is a frontview of a state in which the phases are not aligned with each other.

FIG. 10A is a partial longitudinal sectional view of a constant velocityuniversal joint in which an outer joint member manufactured based on aforging method according to one embodiment of the present invention isincorporated.

FIG. 10B is a side view of the constant velocity universal joint inwhich the outer joint member manufactured based on the forging methodaccording to one embodiment of the present invention is incorporated.

FIG. 11A is a partial longitudinal sectional view of the outer jointmember of the constant velocity universal joint.

FIG. 11B is a side view of the outer joint member of the constantvelocity universal joint.

FIG. 12A is a left side view of an inner joint member of the constantvelocity universal joint.

FIG. 12B is an illustration of inner and outer peripheral surfaces ofthe inner joint member of the constant velocity universal joint.

FIG. 12C is a right side view of the inner joint member of the constantvelocity universal joint.

FIG. 13 is a partial longitudinal sectional view for illustrating thedetails of track grooves of the outer joint member.

FIG. 14 is a longitudinal sectional view for illustrating the details oftrack grooves of the inner joint member.

FIG. 15 is a view for illustrating a state in which the constantvelocity universal joint of FIG. 10A forms a maximum operating angle.

FIG. 16 is a perspective view of the outer joint member as viewed in adirection indicated by the arrows of the line S1-S1 of FIG. 11B.

FIG. 17A is a longitudinal sectional view of a pre-processing materialof the outer joint member in the forging method according to oneembodiment of the present invention.

FIG. 17B is a side view of the pre-processing material of the outerjoint member in the forging method according to one embodiment of thepresent invention.

FIG. 18 is a perspective view of the pre-processing material as viewedin a direction indicated by the arrows of the line S2-N-S2 of FIG. 17B.

FIG. 19 is a partial developed view for illustrating an inner peripheralsurface of the pre-processing material of FIG. 18 .

FIG. 20 is a partial perspective view for illustrating an outerperipheral surface of the pre-processing material of FIG. 18 .

FIG. 21A is an illustration of a forging die, and is a perspective viewof punches.

FIG. 21B is an illustration of the forging die, and is a perspectiveview of a punch base.

FIG. 22A is an illustration of a forming part at a distal end of theforging die of FIGS. 21A, and is a perspective view of the punch.

FIG. 22B is an illustration of the forming part at the distal end of theforging die of FIGS. 21A, and is a developed view of the punch.

FIG. 23 is a perspective view of a distal end portion of the punch base.

FIG. 24A is an illustration of a state in which the punches are combinedwith the punch base, and is a perspective view for illustrating a statein which the punches are radially expanded.

FIG. 24B is an illustration of the state in which the punches arecombined with the punch base, and is a perspective view for illustratinga state in which the punches are radially contracted.

FIG. 25 is a perspective view of a punch holder as viewed inlongitudinal section.

FIG. 26 is a perspective view for illustrating a state in which a die isset.

FIG. 27A is an illustration of a forming step, and is a sectional viewfor illustrating a state in which a workpiece is loaded to a pressmachine.

FIG. 27B is an illustration of the forming step, and is a sectional viewfor illustrating a state in which formation is started.

FIG. 27C is an illustration of the forming step, and is a sectional viewfor illustrating a state in which the formation is completed.

FIG. 28A is an illustration of are moving step, and is a sectional viewfor illustrating a state in which the workpiece is removed from a plate.

FIG. 28B is an illustration of the removing step, and is a sectionalview for illustrating the state in which the workpiece is removed fromthe die.

FIG. 28C is an illustration of the removing step, and is a sectionalview for illustrating the state in which the workpiece is removed fromthe punches.

FIG. 29 is a perspective view of a general outer joint member of aconstant velocity universal joint in partial cross section.

FIG. 30 is a perspective view of a related-art forging apparatus inpartial cross section.

FIG. 31A is an illustration of a punch set of the related-art forgingapparatus, and is a perspective view of a radially expanded state inpartial cross section.

FIG. 31B is an illustration of the punch set of the related-art forgingapparatus, and is a perspective view of a radially contracted state inpartial cross section.

FIG. 32 is a perspective view for illustrating a related-art positioningmechanism.

FIG. 33 is a perspective view of an outer joint member in which trackgrooves each have an arc shape inclined in a circumferential direction,and a diameter of a track groove bottom at a center portion is setlarger than a diameter of a track groove bottom on an opening side of amouth portion in partial cross section.

FIG. 34A is an illustration of a relationship between a pre-processingmaterial and the punch set of the forging apparatus, and is anexplanatory view for illustrating a state in which phases of grooves ofthe pre-processing material and phases of track groove portion formingsurfaces of the punch set are aligned with each other.

FIG. 34B is an illustration of the relationship between thepre-processing material and the punch set of the forging apparatus, andis an explanatory view for illustrating a state in which the phases ofthe grooves of the pre-processing material and the phases of the trackgroove portion forming surfaces of the punch set are not aligned witheach other.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention are describedwith reference to FIG. 1 to FIG. 28 . FIG. 10A is a partial longitudinalsectional view of the constant velocity universal joint, and FIG. 10B isa right side view of FIG. 10A. A constant velocity universal joint 1 isa fixed type constant velocity universal joint, and mainly comprises anouter joint member 2, an inner joint member 3, balls 4 configured totransmit torque, and a cage 5. As illustrated in FIG. 10A, FIG. 10B,FIG. 11 and FIGS. 12 , eight track grooves 7 of the outer joint member 2comprise track grooves 7A and 7B that are inclined in a circumferentialdirection with respect to a joint axial line N-N so that the trackgrooves 7A and 7B adjacent to each other in the circumferentialdirection are inclined in directions opposite to each other. Further,eight track grooves 9 of the inner joint member 3 comprise track grooves9A and 9B that are inclined in the circumferential direction withrespect to the joint axial line N-N so that the track grooves 9A and 9Badjacent to each other in the circumferential direction are inclined indirections opposite to each other. Further, a pair of the track grooves7A and 9A and a pair of the track grooves 7B and 9B of the outer jointmember 2 and the inner joint member 3 are inclined in directionsopposite to each other (mutually opposite), and the eight balls 4 arearranged in crossing portions of the paired track grooves 7A and 9A andthe paired track grooves 7B and 9B of the outer joint member 2 and theinner joint member 3. Detailed description of the track grooves 7 and 9is given later.

A longitudinal section of the joint is illustrated in FIG. 10A. The term“ball raceway center line” is used herein to accurately describe theform and shape of each track groove extending in the axial direction,such as an inclined state and a curved state of the track groove. Theball raceway center line herein refers to a trajectory of the center ofthe ball arranged in the track groove at the time of moving along thetrack groove. Thus, the inclined state of the track groove correspondsto an inclined state of the ball raceway center line, and the arc orlinear shape of the track groove corresponds to an arc or linear shapeof the ball raceway center line.

As illustrated in FIG. 10A, each track groove 7 of the outer jointmember 2 has a ball raceway center line X. The track groove 7 comprisesa first track groove portion 7 a having an arc-shaped ball racewaycenter line Xa about a joint center O defined as a curvature center, anda second track groove portion 7 b having a linear ball raceway centerline Xb. The ball raceway center line Xb of the second track grooveportion 7 b is smoothly continuous with the ball raceway center line Xaof the first track groove portion 7 a as a tangential line. Meanwhile,each track groove 9 of the inner joint member 3 has a ball racewaycenter line Y. The track groove 9 comprises a first track groove portion9 a having an arc-shaped ball raceway center line Ya about the jointcenter O defined as a curvature center, and a second track grooveportion 9 b having a linear ball raceway center line Yb. The ballraceway center line Yb of the second track groove portion 9 b issmoothly continuous with the ball raceway center line Ya of the firsttrack groove portion 9 a as a tangential line.

The curvature centers of the ball raceway center lines Xa and Ya of thefirst track groove portions 7 a and 9 a are arranged on the joint centerO, that is, on the joint axial line N-N. As a result, the track groovedepths can be set equal to each other and the processing can befacilitated. The track grooves 7 and 9 each have an elliptical shape ora Gothic arch shape in transverse section, and the track grooves 7 and 9are held in so-called angular contact with each ball 4 at a contactangle (approximately from 30° to 45°). Thus, the ball 4 is held incontact with side surface sides of the track grooves 7 and 9, which areslightly spaced apart from groove bottoms of the track grooves 7 and 9.

With reference to FIG. 11A and FIG. 11B, detailed description is givenof a state in which the track grooves 7 of the outer joint member 2 areinclined in the circumferential direction with respect to the jointaxial line N-N. FIG. 11A is a partial longitudinal sectional view of theouter joint member 2, and FIG. 11B is a right side view of the outerjoint member 2. The track grooves 7 of the outer joint member 2 aredenoted by the reference symbols 7A and 7B to indicate a difference ininclination direction thereof. As illustrated in FIG. 11A, a plane Mincluding the ball raceway center line X of each track groove 7A and thejoint center O is inclined at an angle γ in the circumferentialdirection with respect to the joint axial line N-N. In addition, in thecase of each track groove 7B adjacent to the track groove 7A in thecircumferential direction, although illustration is omitted, a plane Mincluding the ball raceway center line X of the track groove 7B and thejoint center O is inclined at an angle γ with respect to the joint axialline N-N in an opposite direction to the inclination direction of thetrack groove 7A. In this embodiment, the entire ball raceway center lineX of the track groove 7A, that is, both the ball raceway center line Xaof the first track groove portion 7 a and the ball raceway center lineXb of the second track groove portion 7 b are formed in the plane M.However, the present invention is not limited thereto, and may becarried out in such a mode that only the ball raceway center line Xa ofthe first track groove portion 7 a is included in the plane M.Therefore, it is only required that the plane M including at least theball raceway center line Xa of the first track groove portion 7 a andthe joint center O be inclined in the circumferential direction withrespect to the joint axial line N-N and the first track groove portions7 a adjacent to each other in the circumferential direction be inclinedin directions opposite to each other.

Now, supplementary description is given of the reference symbols of thetrack grooves. The track grooves of the outer joint member 2 as a wholeare denoted by the reference symbol 7. The first track groove portion isdenoted by the reference symbol 7 a. The second track groove portion isdenoted by the reference symbol 7 b. Further, the track groovesdistinguished from each other based on the difference in inclinationdirection are denoted by reference symbols 7A and 7B. First track grooveportions of the respective track grooves 7A and 7B are denoted byreference symbols 7Aa and 7Ba. Second track groove portions of therespective track grooves 7A and 7B are denoted by reference symbols 7Aband 7Bb. The track grooves of the inner joint member 3 described laterare denoted by reference symbols in a similar manner.

Next, with reference to FIG. 12A and FIG. 12B, detailed description isgiven of a state in which the track grooves 9 of the inner joint member3 are inclined in the circumferential direction with respect to thejoint axial line N-N. FIG. 12B is a view of the outer peripheral surfaceof the inner joint member 3. FIG. 12A is a left side view of the innerjoint member 3. FIG. 12C is a right side view of the inner joint member3. The track grooves 9 of the inner joint member 3 are denoted by thereference symbols 9A and 9B to indicate a difference in inclinationdirection thereof. As illustrated in FIG. 13B, a plane Q including theball raceway center line Y of each track groove 9A and the joint centerO is inclined at an angle γ in the circumferential direction withrespect to the joint axial line N-N. In addition, in the case of eachtrack groove 9B adjacent to the track groove 9A in the circumferentialdirection, although illustration is omitted, a plane Q including theball raceway center line Y of the track groove 9B and the joint center Ois inclined at an angle γ with respect to the joint axial line N-N in anopposite direction to the inclination direction of the track groove 9A.It is preferred that the inclination angle γ be set to an angle of from4° to 12° in consideration of operability of the constant velocityuniversal joint 1 and a spherical width F between the closest sides ofthe track grooves of the inner joint member 3. Further, similarly to theouter joint member described above, in this embodiment, the entire ballraceway center line Y of the track groove 9A, that is, both the ballraceway center line Ya of the first track groove portion 9 a and theball raceway center line Yb of the second track groove portion 9 b areformed in the plane Q. However, the present invention is not limitedthereto, and may be carried out in such a mode that only the ballraceway center line Ya of the first track groove portion 9 a is includedin the plane Q. Thus, it is only required that the plane Q including atleast the ball raceway center line Ya of the first track groove portion9 a and the joint center O be inclined in the circumferential directionwith respect to the joint axial line N-N and the first track grooveportions 9 a adjacent to each other in the circumferential direction beinclined in directions opposite to each other. The ball raceway centerline Y of the track groove 9 of the inner joint member 3 is formed so asto be mirror-image symmetrical with the ball raceway center line X ofthe paired track groove 7 of the outer joint member 2 with respect to aplane P that includes the joint center O at an operating angle of 0° andis perpendicular to the joint axial line N-N.

With reference to FIG. 13 , detailed description is given of the trackgrooves as viewed in longitudinal section of the outer joint member 2.The partial longitudinal section of FIG. 13 corresponds to a sectionalview taken along the above-mentioned plane M of FIG. 11A including theball raceway center line X of the track groove 7A and the joint centerO. Thus, in a strict sense, FIG. 13 is not a longitudinal sectional viewtaken along the plane including the joint axial line N-N, but is anillustration of a cross section inclined at the angle γ. In FIG. 13 ,the track groove 7A of the outer joint member 2 is illustrated, and theillustration and description of the track groove 7B are omitted becausethe inclination direction of the track groove 7B is opposite to that ofthe track groove 7A and the other configurations of the track groove 7Bis the same as those of the track groove 7A. A spherical innerperipheral surface 6 of the outer joint member 2 has the track grooves7A formed substantially along the axial direction. Each track groove 7Ahas the ball raceway center line X. The track groove 7A comprises thefirst track groove portion 7Aa having the arc-shaped ball raceway centerline Xa about the joint center O defined as a curvature center (with nooffset in the axial direction), and the second track groove portion 7Abhaving the linear ball raceway center line Xb. In addition, the linearball raceway center line Xb of the second track groove portion 7Ab issmoothly connected, as a tangential line, to an end portion A on anopening side of the ball raceway center line Xa of the first trackgroove portion 7Aa. That is, the end portion A is a connecting pointbetween the first track groove portion 7Aa and the second track grooveportion 7Ab. The end portion A is located on the opening side withrespect to the joint center O, and hence the linear ball raceway centerline Xb of the second track groove portion 7Ab that is connected, as atangential line, to the end portion A on the opening side of the ballraceway center line Xa of the first track groove portion 7Aa is formedso as to approach the joint axial line N-N (see FIG. 10A) as thedistance to the opening side becomes smaller. Thus, it is possible tosecure an effective track length at a maximum operating angle, and tosuppress excessive increase in wedge angle.

As illustrated in FIG. 13 , L represents a straight line connecting theend portion A and the joint center O. A joint axial line N′-N′ projectedonto the plane M including the ball raceway center line X of the trackgroove 7A and the joint center O (see FIG. 11A) is inclined at an angleγ with respect to the joint axial line N-N, and an angle formed betweena perpendicular line K and the straight line L with respect to the jointcenter O on the axial line N′-N′ is represented by β′. Theabove-mentioned perpendicular line K is formed in the plane P includingthe joint center O at the operating angle of 0°. Thus, an angle β formedby the straight line L with respect to the plane P including the jointcenter O at the operating angle of 0° satisfies a relationship of sinβ=sin β′×cos γ.

Similarly, with reference to FIG. 14 , detailed description is given ofthe track grooves as viewed in longitudinal section of the inner jointmember 3. The partial longitudinal section of FIG. 14 corresponds to asectional view taken along the above-mentioned plane Q of FIG. 12Bincluding the ball raceway center line Y of the track groove 9A and thejoint center O. Thus, similarly to FIG. 13 , in a strict sense, FIG. 14is not a longitudinal sectional view in the plane including the jointaxial line N-N, but is an illustration of a cross section inclined atthe angle γ. In FIG. 14 , the track groove 9A of the inner outer jointmember 3 is illustrated, and the illustration and description of thetrack groove 9B are omitted because the inclination direction of thetrack groove 9B is opposite to that of the track groove 9A and the otherconfigurations of the track groove 9B is the same as those of the trackgroove 9A. A spherical outer peripheral surface 8 of the inner jointmember 3 has the track grooves 9A formed substantially along the axialdirection. Each track groove 9A has the ball raceway center line Y. Thetrack groove 9A comprises the first track groove portion 9Aa having thearc-shaped ball raceway center line Ya about the joint center O definedas a curvature center (with no offset in the axial direction), and thesecond track groove portion 9Ab having the linear ball raceway centerline Yb. In addition, the ball raceway center line Yb of the secondtrack groove portion 9Ab is smoothly connected, as a tangential line, toan end portion B on a far side of the ball raceway center line Ya of thefirst track groove portion 9Aa. That is, the end portion B is aconnecting point between the first track groove portion 9Aa and thesecond track groove portion 9Ab. The end portion B is located on the farside with respect to the joint center O, and hence the linear ballraceway center line Yb of the second track groove portion 9Ab that isconnected, as a tangential line, to the end portion B on the far side ofthe ball raceway center line Ya of the first track groove portion 9Aa isformed so as to approach the joint axial line N-N (see FIG. 10A) as thedistance to the far side becomes smaller. Thus, it is possible to securean effective track length at a maximum operating angle, and to suppressexcessive increase in wedge angle.

As illustrated in FIG. 14 , R represents a straight line connecting theend portion B and the joint center O. A joint axial line N′-N′ projectedonto the plane Q including the ball raceway center line Y of the trackgroove 9A and the joint center O (see FIG. 12B) is inclined at an angleγ with respect to the joint axial line N-N, and an angle formed betweena perpendicular line K and the straight line R with respect to the jointcenter O on the axial line N′-N′ is represented by β′. Theabove-mentioned perpendicular line K is formed in the plane P includingthe joint center O at the operating angle of 0°. Thus, an angle β formedby the straight line R with respect to the plane P including the jointcenter O at the operating angle of 0° satisfies a relationship of sinβ=sin β′×cos γ.

Next, description is given of the angle β formed by each of the straightlines L and R with respect to the plane P including the joint center Oat the operating angle of 0°. At an operating angle θ, each ball 4 movesby θ/2 with respect to the plane P including the joint center O in theouter joint member 2 and the inner joint member 3. The angle β isdetermined based on ½ of a frequently used operating angle, and acontact range of the track groove for the ball 4 is determined within arange of the frequently used operating angle. Now, the frequently usedoperating angle is defined. First, a normal angle of the joint refers toan operating angle to be formed in a fixed type constant velocityuniversal joint of a front drive shaft of an automobile with one persononboard when the steering of the automobile is switched to astraightforward mode on a horizontal and flat road surface. In general,the normal angle is selected and determined within a range of from 2° to15° in accordance with design conditions for vehicle types. In addition,the frequently used operating angle refers to an operating angle to beformed in the fixed type constant velocity universal joint of theabove-mentioned automobile during, for example, continuous travel on acurved road, instead of a high operating angle to be formed at the timeof, for example, right and left turns at a traffic intersection. Thisoperating angle is also determined in accordance with the designconditions for vehicle types. The frequently used operating angle issupposed to be 20° at maximum. Thus, the angle β formed by each of thestraight lines L and R with respect to the plane P including the jointcenter O at the operating angle of 0° is set to an angle of 3° to 10°.The angle R is not limited to the angle of from 3° to 10°, and may beset appropriately in accordance with the design conditions for vehicletypes. When the angle β is set to the angle of from 3° to 10°, the fixedtype constant velocity universal joint of this embodiment is widelyapplicable to various vehicle types.

In FIG. 13 , due to the above-mentioned angle β, the end portion A ofthe ball raceway center line Xa of the first track groove portion 7Aacorresponds to a center position of the ball that is moved to the end ofthe opening side along the axial direction at the frequently usedoperating angle. Similarly, in FIG. 14 in the case of the inner jointmember 3, the end portion B of the ball raceway center line Ya of thefirst track groove portion 9Aa corresponds to a center position of theball that is moved to the end of the far side along the axial directionat the frequently used operating angle. With this setting, within therange of the frequently used operating angles, the balls 4 are locatedbetween the first track groove portions 7Aa and 9Aa of the outer jointmember 2 and the inner joint member 3 and between the first track grooveportions 7Ba and 9Ba that are inclined in the opposite directions (seeFIG. 11A and FIG. 12B). Therefore, forces in opposite directions areapplied from the balls 4 to pocket portions 5 a of the cage 5 that areadjacent to each other in the circumferential direction, and hence thecage 5 is stabilized at the position of the joint center O (see FIG.10A). Thus, a contact force between a spherical outer peripheral surface12 of the cage 5 and the spherical inner peripheral surface 6 of theouter joint member 2, and a contact force between a spherical innerperipheral surface 13 of the cage 5 and the spherical outer peripheralsurface 8 of the inner joint member 3 are suppressed. Accordingly, thejoint is smoothly operated under high load and in high speed rotation,and torque loss and heat generation are suppressed. As a result, thedurability is enhanced.

In the constant velocity universal joint 1, the balls 4 may be fittedinto the pocket portions 5 a of the cage 5 with a gap. In this case, itis preferred that the gap be set with a clearance of approximately from0 μm to 40 μm. When the balls 4 are fitted into the pocket portions 5 awith the gap, the balls 4 held in the pocket portions 5 a of the cage 5can smoothly be operated, and hence the torque loss can further bereduced.

In FIG. 15 , a state in which the constant velocity universal joint 1forms the maximum operating angle is illustrated. In each track groove7A of the outer joint member 2, the second track groove portion 7Abhaving the linear ball raceway center line Xb is formed on the openingside. With the second track groove portion 7Ab, the effective tracklength at the maximum operating angle can be secured, and the excessiveincrease in wedge angle can be suppressed in a compact design.Therefore, even when a maximum operating angle θ_(max) is set as high asapproximately 47° as illustrated in FIG. 6 , the contact state can besecured between the ball 4 and the track groove portion 7Ab under astate in which an inlet chamfer 10 having a necessary and sufficientsize is formed, and the increase in wedge angle can be suppressed.

In a range of high operating angles, the balls 4 arranged in thecircumferential direction are temporarily positioned apart between thefirst track groove portions 7Aa and 9Aa (7Ba and 9Ba) (see FIG. 11A andFIG. 12B) and between the second track groove portions 7Ab and 9Ab (7Bband 9Bb) (see FIG. 11A and FIG. 12B). Along with this, the forcesapplied from the balls 4 to the pocket portions 5 a of the cage 5 arenot balanced with each other, and hence the contact forces are generatedbetween the spherical contact portions 12 and 6 of the cage 5 and theouter joint member 2 and between the spherical contact portions 13 and 8of the cage 5 and the inner joint member 3, respectively. However, theangles in the range of high operating angles are used less frequently,and hence the constant velocity universal joint 1 according to thisembodiment is comprehensively capable of suppressing the torque loss andheat generation. Thus, it is possible to attain a compact fixed typeconstant velocity universal joint that is suppressed in torque loss andheat generation, is enhanced inefficiency, is capable of forming highoperating angles, and is excellent in strength and durability at thehigh operating angles.

In the above-mentioned one example of the constant velocity universaljoint, the ball raceway center line Xb of the second track grooveportion 7 b and the ball raceway center line Yb of the second trackgroove portion 9 b each have a linear shape, but the present inventionis not limited thereto. The ball raceway center lines of the secondtrack groove portions may each have a recessed arc shape or a protrudingarc shape having a relatively large curvature radius. Also in this case,an effective track length at a maximum operating angle can be secured,and excessive increase in wedge angle can be suppressed.

The one example and the components of the constant velocity universaljoint, in which the outer joint member manufactured based on the forgingmethod according to the embodiment of the present invention isincorporated, are as described above. Next, the method of forging anouter joint member according to the embodiment of the present inventionis described with reference to FIG. 16 to FIG. 28 .

FIG. 16 is a perspective view of a single finished product of the outerjoint member 2 as viewed in a direction indicated by the arrows of theline S1-S1 of FIG. 11B. The details of the outer joint member 2 are asdescribed above. The outer joint member 2 is formed of carbon steel formachine structural use (for example, S53C) or the like, and a hardenedlayer is formed on a surface of the outer joint member 2 by inductionhardening. In the outer joint member 2, the first track groove portions7 a (7Aa and 7Ba) are formed on the far side, and the second trackgroove portions 7 b (7Ab and 7Bb) are formed on the opening side. Boththe track groove portions are smoothly continuous with each other. Thespherical inner peripheral surface 6 is formed between the track grooves7 (7A and 7B). Turning, spline processing, heat treatment, grinding, andthe like are performed on a forged product after a forming stepdescribed later to obtain the finished product illustrated in FIG. 11 .

This embodiment has a feature in the method of forging theabove-mentioned outer joint member 2. A pre-processing material in theforging method according to this embodiment is described with referenceto FIG. 17 to FIG. 20 . FIG. 17A is a longitudinal sectional view of thepre-processing material. FIG. 17B is a side view of the pre-processingmaterial. FIG. 18 is a perspective view of the pre-processing materialas viewed in a direction indicated by the arrows of the line S2-N-S2 ofFIG. 17B. FIG. 19 is a developed view of an inner peripheral surface ofthe pre-processing material of FIG. 18 . FIG. 20 is a perspective viewof an outer peripheral surface of the pre-processing material of FIG. 18.

The pre-processing material before cold ironing in the forging methodaccording to this embodiment, which is illustrated in FIG. 17A and FIG.17B, is formed by sub-hot forging, and is subjected to surfacelubrication treatment (for example, bonderizing treatment). Apre-processing material W1 comprises a cylindrical portion W1 b and ashaft portion W1 c, and, on an inner peripheral surface of thecylindrical portion W1 b, surfaces 7 a′ (7Aa′ and 7Ba′) having asubstantially finished shape (hereinafter simply referred to as “firsttrack groove surfaces 7 a′ (7Aa′ and 7Ba′) having a substantiallyfinished shape”) corresponding to the first track groove portions 7 a(7Aa and 7Ba) (see FIG. 16 ) are formed in a substantially half part onthe far side from the joint center O of FIG. 17A. Surfaces 7 b′ (7Ab′and 7Bb′) having a preliminary shape (hereinafter simply referred to as“second track groove surfaces 7 b′ (7Ab′ and 7Bb′) having a preliminaryshape”) corresponding to the remaining part from the first track grooveportions 7 a (7Aa and 7Ba) and the second track groove portions 7 b (7Aband 7Bb) having a linear shape are formed in a substantially half parton the opening side from the joint center O of FIG. 17A. The first trackgroove surfaces 7 a′ (7Aa′ and 7Ba′) having a substantially finishedshape are inclined in the circumferential direction, and each have anarc shape about the joint center O defined as a curvature center.Meanwhile, the second track groove surfaces 7 b′ (7Ab′ and 7Bb′) havinga preliminary shape each have a linear shape without inclination in thecircumferential direction.

The first track groove surfaces 7 a′ (7Aa′ and 7Ba′) having asubstantially finished shape of the pre-processing material W1 areformed in the substantially half part on the far side from the jointcenter O. In this configuration, the inclination angle γ of the trackgroove surfaces is relatively small, and the track groove surfaces onthe substantially half part on the far side each have an arc shape aboutthe joint center O defined as the curvature center. Therefore, thepre-processing material W1 can be formed by an integral punch in thesub-hot forging without interference between shoulder portions of thefirst track groove surfaces 7 a′ (7Aa′ and 7Ba′) having a substantiallyfinished shape. With this, increase in forging cost can be suppressed,and the accuracy of the track grooves can be enhanced.

An inner peripheral surface 6′ a having a substantially finished shape(hereinafter simply referred to as “spherical inner peripheral surface6′a having a substantially finished shape”) corresponding to thespherical inner peripheral surface 6 (see FIG. 16 ) is formed in thesubstantially half part on the far side from the joint center O of FIG.17A, and an inner peripheral surface 6′b having a preliminary shape witha substantially cylindrical shape (hereinafter simply referred to as“substantially cylindrical inner peripheral surface 6′b having apreliminary shape”) is formed in the substantially half part on theopening side from the joint center O of FIG. 17A.

In a perspective view of FIG. 18 , the first track groove surfaces 7 a′(7Aa′ and 7Ba′) having a substantially finished shape, the second trackgroove surfaces 7 b′ (7Ab′ and 7Bb′) having a preliminary shape, thespherical inner peripheral surface 6′a having a substantially finishedshape, and the substantially cylindrical inner peripheral surface 6′bhaving a preliminary shape of the pre-processing material W1 areillustrated in a more understandable way. The second track groovesurfaces 7 b′ (7Ab′ and 7Bb′) having a preliminary shape and thesubstantially cylindrical inner peripheral surface 6′b having apreliminary shape each have a tapered shape slightly radially expandedtoward the opening side as a draft of a die.

Further, in a developed view of FIG. 19 , inclined states in thecircumferential direction of the first track groove surfaces 7 a′ (7Aa′and 7Ba′) having a substantially finished shape and the second trackgroove surfaces 7 b′ (7Ab′ and 7Bb′) having a preliminary shape areillustrated in a more understandable way. Ball raceway center lines Xa′of the first track groove surfaces 7 a′ (7Aa′ and 7Ba′) having asubstantially finished shape are each inclined at an angle γ in thecircumferential direction with respect to the joint axial line N-N (seeFIG. 11A). Meanwhile, ball raceway center lines Xb′ of the second trackgroove surfaces 7 b′ (7Ab′ and 7Bb′) having a preliminary shape eachhave a linear shape without inclination in the circumferentialdirection.

As illustrated in FIG. 20 , on the outer peripheral surface of thepre-processing material W1, protruding portions W1 a having a thicknessincreased by partially increasing an outer diameter are formed at fourpositions in the circumferential direction. The protruding portions W1 aare formed so as to secure a sufficient amount of a material at the timeof formation of inclining the second track groove surfaces 7Ab′ and 7Bb′having a preliminary shape of FIG. 18 in opposite directions in thecircumferential direction. In other words, the protruding portions W1 aare formed so as to secure the sufficient amount of the material at thetime of formation of increasing intervals between the second trackgroove surfaces 7Ab′ and 7Bb′ having a preliminary shape in thecircumferential direction on the opening side. Therefore, the protrudingportions W1 a are partially formed in ranges of G1 and G2 illustrated inFIG. 17B, FIG. 18 , and FIG. 20 . The specific shapes of the protrudingportions W1 a are set in consideration of a state of sufficiency of thematerial.

Incidentally, a forging apparatus according to the present inventioncomprises an ironing mechanism M1 (see FIG. 26 and the like) configuredto subject the pre-processing material W1 to cold ironing, and a phaseposition alignment mechanism M2 (see FIG. 1 and the like). The ironingmechanism M1 is described with reference to FIG. 21 to FIG. 26 . FIG.21A is a perspective view for illustrating punches, and FIG. 21B is aperspective view for illustrating a punch base. FIG. 22A is an enlargedperspective view of a distal end portion of the punch, and FIG. 22B is afurther enlarged developed view of an outer peripheral surface of thepunch of FIG. 22A. As illustrated in FIG. 21A and FIG. 22A, punches 20are divided into four parts. On an outer peripheral portion of a distalend of each punch 20, there are formed first track groove portionforming surfaces 27Aa and 27Ba for forming the first track grooveportions 7Aa and 7Ba (see FIG. 16 ), and second track groove portionforming surfaces 27Ab and 27Bb for forming the second track grooveportions 7Ab and 7Bb (see FIG. 16 ). As illustrated in FIG. 22B, thefirst track groove portion forming surfaces 27Aa and 27Ba and the secondtrack groove portion forming surfaces 27Ab and 27Bb are each inclined atan angle γ in the circumferential direction with respect to the jointaxial line N-N (see FIG. 11A). At a position corresponding to theopening side end portion A of the first track groove portions 7Aa and7Ba (see FIG. 13 ), the track groove portion forming surfaces 27Aa and27Ab are continuous with each other, and the track groove portionforming surfaces 27Ba and 27Bb are continuous with each other.

Between the first track groove portion forming surfaces 27Aa and 27Ba, aspherical forming surface 28 for forming the spherical inner peripheralsurface 6 is formed in a region from an axial position of the jointcenter O (see FIG. 11A) to a distal end of the punch 20 (far side of thejoint), and a cylindrical forming surface 29 is formed in a region fromthe spherical forming surface 28 to the axial center side of the punch20 (on the upper side of FIG. 21A and FIG. 22B).

The first track groove portion forming surface 27Aa and the second trackgroove portion forming surface 27Ab are collectively referred to as“track groove forming surface 27A”, and the first track groove portionforming surface 27Ba and the second track groove portion forming surface27Bb are collectively referred to as “track groove forming surface 27B”.

As illustrated in FIG. 21A, an end surface of the punch 20 in thecircumferential direction comprises abutment surfaces 30 to be held inabutment against flange surfaces 36 a (see FIG. 21B) of the punch base21 at the time of radially expanding the punch 20 described later, andstepped surfaces 32 for forming a radial contraction space for thepunches 20, which are formed through tapered stepped portions 31 fromthe abutment surfaces 30. Chamfered portions 33 are formed on theabutment surfaces 30 of each punch 20 so as to suppress nipping of thematerial at the time of formation.

An inner abutment surface 34 to be guided by the punch base 21 is formedon a radially inner side of the punch 20. The four punches 20 areradially contracted to bring the abutment surfaces 30 in thecircumferential direction into abutment against each other. At thistime, a contour of a transverse section formed by the four innerabutment surfaces 34 becomes a square shape. A projecting portion 35 isformed on another end portion of the punch 20 (on the upper side of FIG.21A), and a surface of the projecting portion 35 in the axial directionserves as a positioning tapered stepped portion 44.

In the related art, one punch is arranged for one track groove to besubjected to cold processing. In contrast, in the structure of thisembodiment, the pair of adjacent track groove forming surfaces 27A and27B are arranged in one punch 20. That is, unlike the related-art puncharrangement, a gap between the punches for the pair of adjacent trackgroove forming surfaces 27A and 27B is eliminated, and the pair of trackgroove forming surfaces 27A and 27B are integrally formed on one punch20. Therefore, the sectional area of the punch 20 in this embodiment isabout 3 to 4.5 times larger than the sectional area of the related-artpunch. The sectional area per track groove forming surface is increasedto be 1.5 to 2.25 times larger than that in the related art, and thebending rigidity is increased to be equal to or more than 4.2 timeslarger than that in the related art. That is, with the increase instructural strength and rigidity, formation with high accuracy can beattained. Further, the region having a small thickness of a shoulderportion of the punch is eliminated. Thus, stress concentration isalleviated, thereby being capable of prolonging the life of the die.

Next, the punch base 21 configured to guide the punch 20 so as to enableadvancing and retreating is described with reference to FIG. 21B andFIG. 23 . FIG. 23 is a perspective view of the distal end portion of thepunch base 21 as viewed in a direction different from that in FIG. 21B.The punch base 21 has a substantially quadrangular prism shape, andcomprises four bottom surfaces 37 configured to guide the inner abutmentsurfaces 34 of the punches 20, and flange portions 36 configured toguide the abutment surfaces 30 of the punches 20 in the circumferentialdirection from the corner portions of the four bottom surfaces 37. Theflange surfaces 36 a are formed on both sides of each of the flangeportions 36. On a distal end portion of each of the flange portions 36(on the lower side of FIG. 21B), a tapered surface 38 with a contourcorresponding to that of the chamfered portion 33 of the punch 20described above is formed. On another end portion of the flange portion36 (on the upper side of FIG. 21B), a projecting portion 39 is formed,and a surface of the projecting portion 39 in the axial direction servesas a positioning tapered stepped portion 42. At the center of the punchbase 21, there is formed a through hole 40 through which a shaft portionof an umbrella punch 22 (see FIG. 24B) is inserted so as to enableadvancing and retreating.

In a case of the cold processing in the related art, a punch base in aregion, which corresponds to the track grooves and is close to thedistal end sides of the punches, is thin, and the amount of radialcontraction of the punches is restricted. In this embodiment, the pairof adjacent track groove forming surfaces 27A and 27B are arranged inone punch 20. Therefore, the thickness can be increased as compared tothe related-art punch base. With this, even in a case of an outer jointmember of a constant velocity universal joint that has a large number oftrack grooves and is capable of forming a high operating angle, an outerjoint member of a track groove crossing type that has a required tracklength can be formed.

Further, in the punch base 21, which is reduced in number of groovesformed by the bottom surfaces 37 and the flange surfaces 36 a configuredto guide the punches 20, the sectional shape of the groove is changedfrom the sharp corner shape to the shape of the smooth bottom surface37. Thus, the stress concentration is alleviated, thereby being capableof prolonging the life of the punch base 21. Further, with theabove-mentioned reduction in number of grooves, the rigidity of theintegrated punch base 21 is increased, thereby giving an effect ofenhancing accuracy of a forged product.

Next, an expanding and contracting operation and a relative advancingand retreating operation of the punches 20 and the punch base 21 aredescribed with reference to FIG. 24A and FIG. 24B. FIG. 24A is aperspective view for illustrating a radially expanded state of thepunches 20, and FIG. 24B is a perspective view for illustrating aradially contracted state of the punches 20. A punch set in thedescription and the claims refers to a set including the punches 20 andthe punch base 21 illustrated in FIG. 24A and FIG. 24B, and morepreferably, refers to a set including the punches 20, the punch base 21,and the umbrella punch 22. The punch set is denoted by reference symbolT. As illustrated in FIG. 24A, the flange portions 36 of the punch base21 are inserted between the abutment surfaces 30 (see FIG. 24B) of thepunches 20. At the same time, each of the abutment surfaces 30 and eachof the flange surfaces 36 a are brought into abutment against eachother, and the distal end surfaces of the respective punches 20 and thedistal end surface of the punch base 21 are brought into abutmentagainst a back surface 22 a of the umbrella punch 22 to be arrayed. Withthis, the respective punches 20 are retained with respect to the jointcenter O (see FIG. 10A). This state corresponds to the radially expandedstate of the punches 20.

The respective punches 20 are guided from the radially expanded state ofFIG. 24A along the bottom surfaces 37 and the flange surfaces 36 a ofthe punch base 21 to advance downward. Then, when the distal ends of theflange surfaces 36 a of the punch base 21 pass by the tapered steppedportions 31 of the punches 20, the gap is formed between each of thestepped surfaces 32 (see FIG. 22A) of the punches 20 and each of theflange surfaces 36 a of the punch base 21 so that the radial contractionspace for the punches 20 is secured. In this manner, as illustrated inFIG. 24B, the punches 20 are brought into the radially contracted state.

The expanding and contracting operation and the relative advancing andretreating operation of the punches 20 and the punch base 21 are asdescribed above. Meanwhile, the punches 20 and the punch base 21 arereceived and guided into an inner peripheral hole 41 of a punch holder24 illustrated in FIG. 25 , and perform the relative advancing andretreating operation described above. Specifically, in the innerperipheral hole 41 of the punch holder 24, there are formed axialgrooves 43 in which the projecting portions 39 (see FIG. 21B) of theflange portions 36 of the punch base 21 are slidably fitted, and taperedstopper surfaces 43 a are formed at lower end portions of the axialgrooves 43. The positioning tapered stepped portions 42 of theprojecting portions 39 of the flange portions 36 of the punch base 21are locked to the tapered stopper surfaces 43 a, thereby determining adownward advancing stroke of the punch base 21. The outer peripheralsurfaces of the flange portions 36 of the punch base 21 are guided alongthe inner peripheral hole 41 of the punch holder 24.

In the inner peripheral hole 41 of the punch holder 24, there arefurther formed axial grooves 45 in which the projecting portions 35 ofthe punches 20 (see FIG. 21A) are slidably fitted, and tapered stoppersurfaces 45 a are formed at lower end portions of the axial grooves 45.The positioning tapered stepped portions 44 of the projecting portions35 of the punches 20 are locked to the tapered stopper surfaces 45 a,thereby determining a downward advancing stroke of the punches 20. Outerperipheral surfaces 20 a of the punches 20 are guided along the innerperipheral hole 41 of the punch holder 24.

Due to the tapered stopper surfaces 43 a and the tapered stoppersurfaces 45 a formed in the punch holder 24, the length of the advancingstroke of the punch base 21 is small, and the length of the advancingstroke of the punches 20 is large. With this, after the punch base 21 isstopped, advancement of the punches 20 continues through guiding of theabutment surfaces 30 of the punches 20 along the flange surfaces 36 a ofthe punch base 21, and when the tapered stepped portions 31 of thepunches 20 pass by the distal ends of the flange surfaces 36 a of thepunch base 21, the gap is formed between each of the stepped surfaces 32of the punches 20 and each of the flange surfaces 36 a of the punch base21 so that the radial contraction space for the punches 20 is secured.In this manner, the radially contracting operation of the punches 20 canbe performed with a simple mechanism.

In a perspective view of FIG. 26 , a state in which the die to be usedin the forging method according to this embodiment is set isillustrated. The punches 20 and the punch base 21 are received in thepunch holder 24, and the umbrella punch 22 is inserted through the punchbase 21. A die 23 is mounted and fixed to a slide of a press machinedescribed later together with the punch holder 24. FIG. 26 is anillustration of an arrangement state of the die when the umbrella punch22, the punches 20, and the punch base 21 are inserted in the innerperipheral portion of the pre-processing material W1 and the die 23starts formation of subjecting the outer peripheral portion of thepre-processing material W1 to the ironing (see FIG. 27B).

Next, the specific forming step is described with reference to FIG. 27and FIG. 28 . FIG. 27A to FIG. 27C are illustrations of a process fromloading of the pre-processing material to the completion of formation.FIG. 28A to FIG. 28C are illustrations of a process to removing of theforged product after the completion of formation.

With reference to FIG. 27A, the outlines of the die mounted to the pressmachine and a pressurizing device are described. The die set includingthe die 23 and the punch holder 24 receiving the punch 20, the punchbase 21, the umbrella punch 22, and the like, a pressurizing cylinder51, and a knockout cylinder 52 are mounted and fixed to a slide 50configured to be raised and lowered by, for example, a hydraulic drivesource of the press machine. The punches 20, the punch base 21, theumbrella punch 22, and a pressing member 53 are slidably received insidethe punch holder 24. A shaft portion 22 b of the umbrella punch 22 isslidably fitted through a through hole 53 a formed at the center of thepressing member 53. The shaft portion 22 b of the umbrella punch 22 iscoupled to a rod 52 a of the knockout cylinder 52 through intermediationof a spring receiving member 54. A spring receiving portion 53 b isformed on an upper surface of the pressing member 53, and a compressioncoil spring 55 is incorporated between the spring receiving portion 53 band the spring receiving member 54. Due to an urging force of thecompression coil spring 55, the punches 20 and the punch base 21 areretained and arrayed between the back surface 22 a of the umbrella punch22 and a lower surface 53 c of the pressing member 53. The pressurizingcylinder 51 presses the pressing member 53 through intermediation of acoupling member 56. A plate 57 is mounted and fixed to a lower portionof the press machine, and the pre-processing material W1 is set on theplate 57.

Detailed description is given of the forming step. As illustrated inFIG. 27A, in a state in which a workpiece is loaded, the slide 50 ispositioned at a top dead center, and a certain pressure is applied tothe pressurizing cylinder 51, whereas a pressure is not applied to theknockout cylinder 52. The pressure state of the pressurizing cylinder 51and the knockout cylinder 52 is maintained until the completion offormation. In this state, the pre-processing material W1 is set on theplate 57 so as to align a phase thereof with phases of the punches 20.

After the workpiece is loaded, as illustrated in FIG. 27B, in a state inwhich formation is started, the pressurizing cylinder 51 is in a stateof receiving a certain pressure load so that the slide 50 is lowered,the umbrella punch 22 is brought into abutment against a cup bottomsurface of the pre-processing material W1 while keeping a constantpressure, and the slide 50 is lowered up to a position at which anopening end portion of the pre-processing material W1 faces a die hole23 a of the die 23.

In the state in which the umbrella punch 22 is held in abutment againstthe cup bottom surface of the pre-processing material W1 while keepingthe constant pressure, and the axial positions of the track grooveforming surfaces 27A and 27B of each of the punches 20 are stabilized,as illustrated in FIG. 27C, the die 23 is lowered to press the outerperipheral surface from the opening side of the pre-processing materialW1, the slide 50 reaches a bottom dead center, and the inner peripheralportion of the pre-processing material W1 is pressed against the trackgroove forming surfaces 27A and 27B, the spherical forming surface 28,and the cylindrical forming surface 29 of each of the punches 20. Inthis manner, finishing formation of the track groove surfaces 7 a′ and 7b′, the spherical inner peripheral surface 6′a on the far side, and thecylindrical inner peripheral surface 6′b on the opening side in theentire region in the axial direction is completed.

Specifically, on the far side of the pre-processing material W1, thefirst track groove surfaces 7 a′ (7Aa′ and 7Ba′) having a substantiallyfinished shape become first track groove surfaces 7 a″ (7Aa″ and 7Ba″)having a finished shape, and the spherical inner peripheral surface 6′ ahaving a substantially finished shape becomes a spherical innerperipheral surface 6″ a having a finished shape. Further, on the openingside of the pre-processing material W1, the second track groove surfaces7 b′ (7Ab′ and 7Bb′) having a preliminary shape become second trackgroove surfaces 7 b″ (7Ab″ and 7Bb″) having a finished shape, and thesubstantially cylindrical inner peripheral surface 6′b having apreliminary shape becomes a substantially cylindrical inner peripheralsurface 6″b having a finished shape. The finished shape in thedescription refers to a shape to be kept in the forged product.

In the above-mentioned formation, the protruding portions W1 a areformed on the pre-processing material W1. Thus, a sufficient amount ofthe material is secured at the time of formation of increasing theintervals between the second track groove surfaces 7Ab′ and 7Bb′ havinga preliminary shape in the circumferential direction on the openingside.

Due to a springback phenomenon after the completion of formation, aforged product W2 is in a state of being held by the die 23. Asdescribed above, through the ironing in which the die 23 presses andpushes the outer peripheral surface from the opening portion side of thepre-processing material W1, the material sufficiency at the innerperipheral portion of the pre-processing material W1 can be enhanced.With the structure in which the above-mentioned pair of track grooveforming surfaces 27A and 27B are integrally formed on one punch 20 andthe ironing involving pushing from the opening portion side of thecylindrical portion W1 b of the pre-processing material W1, formationwith high accuracy, prolongment in life of the die, and the like can befurther promoted.

After the completion of formation, a removing step for the forgedproduct W2 is performed. The pressure applied by the pressurizingcylinder 51 is relieved so that the pressure applied by the umbrellapunch 22 to the cup bottom surface of the forged product W2 iseliminated. Then, as illustrated in FIG. 28A, the slide 50 is raised sothat the forged product W2, the punches 20, the punch base 21, and theumbrella punch 22, which are held inside the die 23, are raised. Thus,the forged product W2 is removed from the plate 57 so that the slide 50reaches the top dead center.

After that, as illustrated in FIG. 28B, the pressure is applied to thepressurizing cylinder 51 so that the umbrella punch 22 presses the cupbottom surface of the forged product W2 through intermediation of thepunches 20 and the punch base 21, and the forged product W2 is separatedfrom the die 23. When the punch base 21 is lowered up to this state, thetapered stepped portions 42 of the punch base 21 are locked to thetapered stopper surfaces 43 a of the punch holder 24, and the loweringoperation of the punch base 21 is stopped.

After that, as illustrated in FIG. 28C, the pressure is applied to theknockout cylinder 52 so that the punches 20 designed to have a steplength larger than the process length of the punch base 21 are furtherlowered. Then, the positioning tapered stepped portions 44 of thepunches 20 are locked to the tapered stopper surfaces 45 a of the punchholder 24, and the stepped surfaces 32 of the punches 20 reach thedistal end portions of the flange portions 36 of the punch base 21. Withthis, the gap is formed between each of the stepped surfaces 32 (seeFIG. 22A) of the punches 20 and each of the flange surfaces 36 a (seeFIG. 21B) of the punch base 21 so that the punches 20 are radiallycontracted and the forged product W2 is removed. The forged product W2is then subjected to turning, spline processing, heat treatment,grinding, and the like to be processed into the finished productillustrated in FIG. 12 .

The forging method according to this embodiment is completed through theabove-mentioned processes of FIG. 27A to FIG. 27C and FIG. 28A to FIG.28C. With the forging method according to this embodiment, in the outerjoint member of the constant velocity universal joint, which comprisesthe track grooves having an arc shape and being inclined in thecircumferential direction, the track grooves with high accuracy can beformed while a forging tool can be reduced in cost and be prolonged inlife.

Incidentally, this forging apparatus comprises the phase alignmentmechanism M2 as illustrated in FIG. 1 . The phase alignment mechanism M2comprises a plate 201, a pair of phase alignment jigs 203 and 203, apressing member (spring member) 204, and a rotary mechanism M comprisinga shaft 205. The plate 201 is configured to support the pre-processingmaterial W1. The pair of phase alignment jigs 203 and 203 are providedupright from a pin holder 202. The pressing member (spring member) 204is configured to raise the pin holder 202 and the phase alignment jigs203 and 203 through elastic pressing. The shaft 205 is configured torotationally drive. Further, the phase alignment jigs 203 and 203 areinserted through a head 206 provided at a distal end portion of theshaft 205. Therefore, the head 206 rotates along with rotation of theshaft 205, and the phase alignment jigs 203 and 203 rotate about anaxial center of the shaft. The pressing member (spring member) 204 issuppressed in an urging force thereof by a stopper mechanism (forexample, a cylinder mechanism) (not shown).

As described above, in the material W1 in this case, on the innerperipheral surface of the cylindrical portion W1 b, the first trackgroove surfaces 7 a′ (7Aa′ and 7Ba′) having a substantially finishedshape are formed in the substantially half part on the far side from thejoint center O of FIG. 10A. The second track groove surfaces 7 b′ (7Ab′and 7Bb′) having a preliminary shape are formed in the substantiallyhalf part on the opening side from the joint center O of FIG. 10A.Further, the first track groove surfaces 7 a′ (7Aa′ and 7Ba′) having asubstantially finished shape are inclined in the circumferentialdirection, and each have an arc shape about the joint center O definedas a curvature center. Meanwhile, the second track groove surfaces 7 b′(7Ab′ and 7Bb′) having a preliminary shape each have a linear shapewithout inclination in the circumferential direction.

Therefore, openings of the grooves of the pre-processing material W1(openings of the second track groove surfaces 7 b′) are arranged atequal pitches along the circumferential direction. As illustrated inFIG. 3 , in an inlet portion of the inner peripheral surface of thecylindrical portion W1 b, portions each between the track groovesurfaces 7Ab′ and 7Bb′ adjacent in the circumferential direction arethin portions Ta or thick portions Tb, and the thin portions Ta and thethick portions Tb are alternately arranged along the circumferentialdirection.

The phase alignment jigs 203 and 203 are arranged in directions oppositeto each other at 180° with respect to the axial center of the pin holder202. As illustrated in FIG. 5 , each of the phase alignment jigs 203comprises a shaft member 207, and a main body portion 208 providedupright from the shaft member 207. The main body portion 208 comprises aflat plate-shaped body having a flat convex curved surface, and convexraised portions formed on end portions on the surface of the flatplate-shaped body. In this case, the convex raised portions correspondto convex portions 210 and 210 to be fitted to the openings of thesecond track groove surfaces 7Ab′ and 7Bb′, and the flat plate-shapedbody of the main body portion 208 corresponds to a coupling portion 211configured to couple the convex portions 210 and 210 to each other. Theshaft member 207 comprises a shaft main body 207 a, and a flange portion207 b provided at a lower end of the shaft main body 207 a.

Incidentally, as illustrated in FIG. 1 , the pin holder 202 comprises adisc portion 202 a, and a shaft portion 202 b suspended from a centerportion of the disc portion 202 a. The disc portion 202 a comprises adisc portion main body 215, and a lid member 216 fixed to the discportion main body 215. In this case, the pin holder 202 can be raised byan elastic force of a pressing member (spring member) 204, but an urgingforce of the pressing member is suppressed by a stopper mechanism (forexample, a cylinder mechanism) (not shown).

The head 206 comprises a head main body 206 a formed of a short columnarbody, and the head main body 206 a has through holes 212 and 212arranged in directions opposite to each other at 180°. The pair of phasealignment jigs 203 and 203 are fitted into the through holes 212 and212. Further, the head main body 206 a of the head 206 is fitted to athrough hole 201 a of the plate 201.

Next, a positioning method for the pre-processing material W1 with useof the positioning mechanism M2 illustrated in FIG. 1 and FIG. 2 isdescribed. First, the positioning mechanism M2 is brought into aninitial state. The initial state is a state in which the urging force ofthe pressing member (spring member) 204 is suppressed by the stoppermechanism, and the pair of phase alignment jigs 203 and 203 providedupright from the pin holder 202 are set so that distal ends thereof arelocated below the upper surface of the head 206.

Then, the pre-processing material W1 is moved and is held at a positionconcentric with the head 206. In this state, an opening end surface ofthe cylindrical portion W1 b of the pre-processing material W1 is placedon the plate 201. In this state, the urging force of the pressing member(spring member) 204 is released, and the pin holder 202 and the phasealignment pins 153 and 153 are raised.

In this case, when portions each between the grooves adjacent to eachother in the circumferential direction, which are to be fitted to theconvex portions 210 and 210 of the phase alignment jigs 203 and 203,correspond to the thick portions Tb as illustrated in FIG. 6 , each ofthe phase alignment jigs 203 and 203 cannot be fitted to the opening ofthe cylindrical portion W1 b of the pre-processing material W1.Meanwhile, when portions each between the grooves adjacent to each otherin the circumferential direction, which are to be fitted to the convexportions 210 and 210 of the phase alignment jigs 203 and 203, correspondto the thin portions Ta as illustrated in FIG. 7 , each of the phasealignment jigs 203 and 203 cannot be fitted to the opening of thecylindrical portion W1 b of the pre-processing material W1.

When each of the phase alignment jigs 203 and 203 can be fitted to theopening of the cylindrical portion W1 b of the pre-processing materialW1 as illustrated in FIG. 7 , the convex portions 210 and 210 of thephase alignment jigs 203 and 203 are fitted to the grooves (7Ab′ and7Bb′) adjacent to each other in the circumferential direction, and thecoupling portions 211 each between the convex portions 210 and 210 areinternally fitted to the thin portions Ta. In this state, thepre-processing material W1 is rotated about its axial center throughrotation of the shaft 205, and is stopped at a position at which phasesof the pre-processing material W1 are aligned with phases of the punches20. That is, phases of the track grooves 7A′ and 7B′ of the material arealigned with phases of the track groove portion forming surfaces 27A and27B of the punches 20.

Further, as illustrated in FIG. 6 , when portions adjacent to each otherin the circumferential direction, which are to be fitted to the convexportions 210 and 210 of the position alignment jigs 203 and 203,correspond to the thick portions Tb as illustrated in FIG. 6 , each ofthe phase alignment jigs 203 and 203 cannot be fitted to the opening ofthe cylindrical portion W1 b of the pre-processing material W1. Thus,the pre-processing material W1 is rotated about its axial center throughrotation of the shaft 205 (see FIG. 1 ) so that the coupling portions211 each between the convex portions 210 and 210 are internally fittedto the thin portions Ta. After that, the pre-processing material W1 isrotated about its axial center through rotation of the shaft 205, and isstopped at a position at which the phases of the pre-processing materialW1 are aligned with the phases of the punches 20. That is, phases of thegrooves 7Ab′ and 7Bb′ of the pre-processing material W1 are aligned withthe phases of the track groove portion forming surfaces 27A and 27B ofthe punches 20.

Then, under the state in which the phases of the grooves 7Ab′ and 7Bb′of the pre-processing material W1 are aligned with the phases of thetrack groove portion forming surfaces 27A and 27B of the punches 20, thepre-processing material W1 is set to the ironing mechanism M1 byconveying means (for example, an XYZ robot arm or the like) (not shown)while maintaining the state. With this, under the state in which thephases of the grooves 7Ab′ and 7Bb′ of the pre-processing material W1and the phases of the track groove portion forming surfaces 27A and 27Bof the punches 20 are aligned with each other, the pre-processingmaterial W1 can be set to the ironing mechanism M1. When thepre-processing material W1 can be set to the ironing mechanism M1, theironing described above can be performed.

FIG. 9A is an illustration of the state in which the phases of thegrooves 7Ab′ and 7Bb′ of the pre-processing material W1 and the phasesof the track groove portion forming surfaces 27A and 27B of the punches20 are aligned with each other. FIG. 9B is an illustration of the statein which the phases of the grooves 7Aa′ and 7Ab′ of the pre-processingmaterial W1 and the phases of the track groove portion forming surfaces27A and 27B of the punches 20 are not aligned with each other.

A part of the punch set T illustrated in FIG. 8 below the track grooveportion forming surfaces 27A and 27B of the punches 20 is embedded inabasement 225. Therefore, the punch set T comprises the umbrella punch22 in addition to the punches 20 and the punch base 21 similarly to thatillustrated in FIG. 12 to FIG. 17 . Therefore, as illustrated in FIG. 26, ironing can be performed with use of the punches 20 and the die 23.Therefore, the punch set T does not comprise the basement 225.

As described above, the phase alignment mechanism M2 comprises theposition alignment jigs 203 and 203 each comprising the pair of convexportions 210 and 210, which are to be fitted to the two grooves of thepre-processing material which are adjacent to each other in thecircumferential direction under the state in which the phases of thegrooves 7Ab′ and 7Bb′ in the inner peripheral surface of thepre-processing material W1 and the phases of the track groove portionforming surfaces 27A and 28B of the punches 20 are aligned with eachother, and are restricted from being fitted thereto under the state inwhich those phases are not aligned with each other.

With the forging apparatus for an outer joint member of a constantvelocity universal joint according to the present invention, before thepre-processing material W1 is fitted to the punch 20, the phases of thegrooves 7Ab′ and 7Bb′ in the inner peripheral surface of thepre-processing material W1 and the phases of the track groove portionforming surfaces 27A and 27B of the punch 20 can be aligned with eachother by the phase alignment mechanism M2. Thus, in the ironingmechanism M1, under the state in which the phases of the grooves 7Ab′and 7Bb′ of the pre-processing material W1 and the phases of the trackgroove portion forming surfaces 27A and 27B of the punch set are alignedwith each other, the punch 20 can be press-fitted into the cylindricalportion W1 b. Accordingly, forming failure, die breakage, and the likecan be prevented. Further, the ironing mechanism M1 comprises the punch20 that is fitted into the cylindrical portion W1 b of thepre-processing material W1 and is radially expandable and contractible,and the die 23 having the hole 23 a into which the cylindrical portionW1 b is fitted. Accordingly, an existing ironing mechanism (forgingapparatus) M1 can be used as it is. Therefore, cost reduction can beattained.

Although the embodiment of the present invention has been describedabove, the present invention is not limited to the embodiment describedabove, and various modifications may be made thereto. The number ofpositioning jigs 203 and 203 is not limited to two and it is onlyrequired to provide at least one positioning jig 203. Further, as theouter joint member, in the embodiment, the number of track grooves iseight, and the number of balls serving as torque transmission members ofthe constant velocity universal joint is eight, but may be six or ten ormore.

As the position alignment mechanism M2, in the embodiment describedabove, the inner diameter (portion excluding the grooves 7Ab′ and 7Bb′)of the inner peripheral surface of the cylindrical portion W1 b of thepre-processing material W1 comprises a large-diameter portion and asmall-diameter portion, and the pre-processing material W1 has such ashape that the positioning jigs 203 can be inserted when the positioningjigs 203 correspond to the large-diameter portion, and cannot beinserted when the positioning jigs 203 correspond to the small-diameterportion. However, the present invention is not limited thereto. That is,a convex and concave fitting structure may be employed. In this case,convex portions may be provided on the pre-processing material W1 side,and concave portions may be provided on the positioning jig 203 side.Conversely, concave portions may be provided on the pre-processingmaterial W1 side, and convex portions may be provided on the positioningjig 203 side.

INDUSTRIAL APPLICABILITY

As the constant velocity universal joint, there is provided the fixedtype constant velocity universal joint in which the balls are used asthe torque transmission members. The track grooves each have an arcshape that is inclined in the circumferential direction. It is possibleto form the outer joint member in which the diameter of the track groovebottom at the center portion is set larger than the diameter of thetrack groove bottom on the opening side.

REFERENCE SIGNS LIST

-   1 constant velocity universal joint-   2 outer joint member-   3 inner joint member-   4 ball-   5 cage-   6 spherical inner peripheral surface-   7 track groove-   7 a′ first track groove surface having substantially finished shape-   7 b′ second track groove surface having preliminary shape-   8 spherical outer peripheral surface-   9 track groove-   12 spherical outer peripheral surface-   13 spherical inner peripheral surface-   20 punch-   21 punch base-   22 umbrella punch-   23 die-   23 a die hole-   24 punch holder-   27A, 27B track groove forming surface-   27Aa, 27Ba first track groove portion forming surface-   27Ab, 27Bb second track groove portion forming surface-   203 phase alignment jig-   M1 ironing mechanism-   M2 phase alignment mechanism-   M rotary mechanism-   T punch set-   Ta thin portion-   Tb thick portion-   W1 pre-processing material-   W1 a protruding portion-   W1 b cylindrical portion

1-11. (canceled)
 12. A forging method for an outer joint member of aconstant velocity universal joint, the constant velocity universal jointcomprising: an outer joint member having a spherical inner peripheralsurface in which a plurality of track grooves are formed; an inner jointmember having a spherical outer peripheral surface in which a pluralityof track grooves are formed so as to be paired with the track grooves ofthe outer joint member; a plurality of balls, which are interposedbetween the track grooves of the outer joint member and the trackgrooves of the inner joint member, and are configured to transmittorque; and a cage, which is interposed between the spherical innerperipheral surface of the outer joint member and the spherical outerperipheral surface of the inner joint member, and is configured to holdthe balls, the track grooves of the outer joint member and the trackgrooves of the inner joint member each having an arc-shaped ball racewaycenter line having a curvature center that is prevented from beingoffset in an axial direction with respect to a joint center, a planeincluding the ball raceway center line and the joint center beinginclined in a circumferential direction with respect to a joint axialline, each of the track grooves of the outer joint member and each ofthe track grooves of the inner joint member, which are paired with eachother, being inclined in mutually opposite directions, the forgingmethod comprising: aligning, before a pre-processing material is fittedinto a punch set, phases of grooves formed in an inner peripheralsurface of a cylindrical portion of the pre-processing material andphases of track groove portion forming surfaces of the punch set witheach other with use of a phase alignment mechanism; and performingironing by fitting the punch set that is radially expandable andcontractible into the cylindrical portion of the pre-processing materialof the outer joint member comprising the cylindrical portion under astate in which the phases are aligned with each other, and press-fittingthe cylindrical portion into a hole of a die, and the phase alignmentmechanism comprising a phase alignment jig comprising a pair of convexportions, which are to be fitted into two grooves of the pre-processingmaterial which are adjacent to each other in the circumferentialdirection under a state in which the phases of the grooves in the innerperipheral surface of the pre-processing material and the phases of thetrack groove portion forming surfaces of the punch set are aligned witheach other, and are restricted from being fitted thereto under a statein which the phases of the grooves in the inner peripheral surface ofthe pre-processing material and the phases of the track groove portionforming surfaces of the punch set are not aligned with each other. 13.The forging method for an outer joint member of a constant velocityuniversal joint according to claim 12, wherein the inner peripheralsurface of the cylindrical portion of the pre-processing material has:an arc-shaped track groove surface having a substantially finished shapeand being formed in a substantially half part in an axial direction on afar side so as to be inclined in the circumferential direction; and alinear track groove surface having a preliminary shape and being formedin a substantially half part in the axial direction on an opening sideso as to be prevented from being inclined in the circumferentialdirection, wherein, in an inlet portion of the inner peripheral surfaceof the cylindrical portion, portions of the pre-processing material eachbetween the grooves adjacent to each other in the circumferentialdirection are thin portions or thick portions, and the thin portions andthe thick portions are alternately arranged along the circumferentialdirection, and wherein the phase alignment mechanism comprises a phasealignment jig comprising: a pair of convex portions to be fitted alongthe axial direction to the grooves of the pre-processing material whichare adjacent to each other in the circumferential direction; and acoupling portion, which is formed between the convex portions, isallowed to be internally fitted to corresponding one of the thinportions of the pre-processing material along the axial direction, andis prevented from being internally fitted to corresponding one of thethick portions of the pre-processing material along the axial direction.14. The forging method for an outer joint member of a constant velocityuniversal joint according to claim 12, wherein, under a state in whichthe pair of convex portions of the phase alignment jig are fitted to apair of grooves of the pre-processing material, and a radially outersurface of the phase alignment jig is internally fitted to thecorresponding one of the thick portions, the pre-processing material isstopped at a predetermined phase position through rotation of the phasealignment jig, and ironing with the punch set and the die is performed.15. The forging method for an outer joint member of a constant velocityuniversal joint according to claim 12, wherein, in the ironing, thecylindrical portion of the pre-processing material is press-fitted intothe hole of the die from an opening portion side of the cylindricalportion.
 16. The forging method for an outer joint member of a constantvelocity universal joint according to claim 13, wherein, under a statein which the pair of convex portions of the phase alignment jig arefitted to a pair of grooves of the pre-processing material, and aradially outer surface of the phase alignment jig is internally fittedto the corresponding one of the thick portions, the pre-processingmaterial is stopped at a predetermined phase position through rotationof the phase alignment jig, and ironing with the punch set and the dieis performed.
 17. The forging method for an outer joint member of aconstant velocity universal joint according to claim 13, wherein, in theironing, the cylindrical portion of the pre-processing material ispress-fitted into the hole of the die from an opening portion side ofthe cylindrical portion.
 18. The forging method for an outer jointmember of a constant velocity universal joint according to claim 14,wherein, in the ironing, the cylindrical portion of the pre-processingmaterial is press-fitted into the hole of the die from an openingportion side of the cylindrical portion.